Turbo Expander System Behavior Improvement Using an Adaptive Fuzzy PID Controller

Turbo-expanders are used in industries for cooling, liquefaction and also power generation. An important part of these turbines is the variable angle nozzle causing a nonlinear behavior that is not well recognized among the prime movers of the dispersed generators. In this paper, at first, the turbo expander system is evaluated in details and its nonlinear behavior is investigated. Then, the system is linearized and variations of its eigenvalues are investigated by a system modal analysis for some changes in input gas stream parameters. Afterwards, variations of nozzle angle and output pressure are studied using a conventional PID controller. Due to system nonlinearity, adaptive PID and fuzzy controllers are then designed to improve the system behavior by controlling mechanical parts of turbine nozzle actuator. An adaptive controller uses fuzzy system as a nonlinear tuner that specifies the coefficients for conventional PID controller of the system. A comparison of controllers’ effects is presented. Simulation results show that the turbine response to step changes in gas flow rate or pressure would be more steady when the adaptive or fuzzy controllers are used.